1. Field of the Invention
The invention pertains to the art of rotary compressors and in particular to vane assemblies therefor.
2. Description of the Prior Art
The provision of vane assemblies which include a blade portion and a pivotal shoe portion on the distal edge of the blade in rotary devices such as pumps, engines and compressors is known as evidenced by U.S. Pat. Nos. 40,008; 832,848; 856,739; 2,458,620; and 3,193,192. In each of these patents there is disclosed a vane assembly with a blade and shoe joined in a cylinder and socket type joint. However, in each case the cylinder portion of the joint is provided in the shoe and the socket portion is provided in the edge of the blade. In all of the arrangements except U.S. Pat. No. 2,458,620, the part of the shoe which bears against a surface with which there is relative velocity is separated from the cylindrical portion of the shoe by a neck. In such arrangements it is possible for the bearing part of the shoe to be provided with an extended surface in a transverse direction which has both advantages and disadvantages in respects which will be detailed later.
In the case of the other patent, the shoe is semi-cylindrical in cross section with the rounded portion fitting within the socket at the edge of the vane, and the flattened portion having a curvature stated to correspond to the curvature of the main cylinder wall. While this arrangement may be advantageous in reducing turning moments tending toward instability, the arrangement also precludes the use of an extended surface in a transverse direction, which is beneficial with respect to obtaining a hydrodynamic lubricating film between the shoe and the surface against which it bears and which has relative movement.
It is the aim of this invention to provide a rotary compressor having an improved vane assembly of the blade and shoe type. The improvement resides largely in the provision of a structure which promotes attaining a good hydrodynamic lubricating film between the shoe surface and the surface with which there is relative movement. The attainment of this hydrodynamic film through the particular structure of this invention is due in part at least to the structure being of a character in which the turning moment applied to the shoe is reduced relative to the moments applied to the prior art shoes.
It is believed that a better understanding of the invention will be gained if some basic geometric phenomena as related to hydrodynamic films is understood. The purpose of the presence of a good hydrodynamic film is of course to give good lubrication between relatively moving parts. The quality of lubrication obtained is in part at least a function of the area extent of the hydrodynamic film present. Thus, a pair of completely flat opposed surfaces with a hydrodynamic film between will provide the maximum lubricating quality. The lubricating quality is reduced if one of the surfaces has a radius, and to the extent that the radius becomes smaller and smaller, the quality of the lubrication is further reduced. Also, two curved surfaces are inferior to one flat and one curved surface having the same radius as the two curved surfaces. To the extent the radii decrease, the quality of lubrication is correspondingly reduced.
Another factor which bears on the quality of the hydrodynamic film is the load which is imposed upon the two facing surfaces between which relative movement exists. Thus, to the extent that the load may be reduced while still maintaining an adequate seal, this is a preferable arrangement. Since a component of the load with a sliding shoe arrangement of any type includes the moment tending to pivot the shoe, an arrangement in which the moment is kept to the minimum reasonable value is preferable.
A feature of the invention is the provision of a structure in which the moment is reduced relative to the prior art structures without sacrificing the disadvantage of a reduced area of shoe sliding surface.